U.S. patent number 8,884,561 [Application Number 13/818,120] was granted by the patent office on 2014-11-11 for ac motor driving apparatus.
This patent grant is currently assigned to Mitsubishi Electric Corporation. The grantee listed for this patent is Shinichi Furutani, Jun Hattori, Manabu Ohashi, Akiko Tabuchi, Kazuhiko Tsutsui, Yoji Tsutsumishita. Invention is credited to Shinichi Furutani, Jun Hattori, Manabu Ohashi, Akiko Tabuchi, Kazuhiko Tsutsui, Yoji Tsutsumishita.
United States Patent |
8,884,561 |
Furutani , et al. |
November 11, 2014 |
AC motor driving apparatus
Abstract
In the case where DC power from a DC power supply is converted
to AC power by an inverter and supplied to an AC motor, a power
compensator is connected in parallel with a DC power input portion
of the inverter, and a control device of the power compensator
charges/discharges a power storage device to perform a power
compensation process A when power demand for the AC motor exceeds a
predetermined value, and takes into account power allowance which
can be inputted and outputted from the DC power supply to the power
storage device and performs a power storage adjustment process B of
performing auxiliary charge of the power storage device within the
range of the power allowance when the power compensation process A
is unnecessary.
Inventors: |
Furutani; Shinichi (Tokyo,
JP), Tabuchi; Akiko (Tokyo, JP), Tsutsui;
Kazuhiko (Tokyo, JP), Tsutsumishita; Yoji (Tokyo,
JP), Hattori; Jun (Tokyo, JP), Ohashi;
Manabu (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Furutani; Shinichi
Tabuchi; Akiko
Tsutsui; Kazuhiko
Tsutsumishita; Yoji
Hattori; Jun
Ohashi; Manabu |
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo |
N/A
N/A
N/A
N/A
N/A
N/A |
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
Mitsubishi Electric Corporation
(Tokyo, JP)
|
Family
ID: |
45810215 |
Appl.
No.: |
13/818,120 |
Filed: |
September 6, 2010 |
PCT
Filed: |
September 06, 2010 |
PCT No.: |
PCT/JP2010/065221 |
371(c)(1),(2),(4) Date: |
February 21, 2013 |
PCT
Pub. No.: |
WO2012/032589 |
PCT
Pub. Date: |
March 15, 2012 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20130154531 A1 |
Jun 20, 2013 |
|
Current U.S.
Class: |
318/400.26 |
Current CPC
Class: |
B60L
7/14 (20130101); B60L 50/51 (20190201); H02J
7/34 (20130101); B60L 15/007 (20130101); H02P
27/06 (20130101); B60L 50/40 (20190201); B60L
3/003 (20130101); B29C 2045/7673 (20130101); Y02T
10/64 (20130101); Y02T 10/644 (20130101); Y02T
10/70 (20130101); H02P 2201/09 (20130101); H02P
2201/07 (20130101); Y02T 10/7022 (20130101); Y02T
10/645 (20130101); Y02T 10/7005 (20130101); H02M
5/458 (20130101); Y02P 70/10 (20151101); Y02P
70/261 (20151101); B60L 2210/10 (20130101); Y02T
10/7216 (20130101); B60L 2240/545 (20130101); Y02T
10/72 (20130101); Y02P 70/26 (20151101) |
Current International
Class: |
H02P
6/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001 139244 |
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May 2001 |
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JP |
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2001 186689 |
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Jul 2001 |
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JP |
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2001 320893 |
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Nov 2001 |
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JP |
|
2004 343826 |
|
Dec 2004 |
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JP |
|
2005 328618 |
|
Nov 2005 |
|
JP |
|
2009 136058 |
|
Jun 2009 |
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JP |
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4339916 |
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Oct 2009 |
|
JP |
|
Other References
Office Action and Search Report issued Sep. 18, 2013 in Taiwanese
Patent Application No. 100124549 (with partial English
translation). cited by applicant .
Kuo-Hen Chao, et al., "New Control Methods for Single Phase PWM
Regenerative Rectifier with Power Decoupling Function," PEDS2009,
Nov. 2-5, 2009, pp. 1091-1096. cited by applicant .
International Search Report Issued Nov. 22, 2010 in PCT/JP10/65221
Filed Sep. 6, 2010. cited by applicant.
|
Primary Examiner: Ro; Bentsu
Assistant Examiner: Imtiaz; Zoheb
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Claims
The invention claimed is:
1. An AC motor driving apparatus comprising: a DC power supply
which supplies DC power; an inverter which is connected to the DC
power supply via a DC bus bar and converts the DC power to AC power
and supplies the AC power to an AC motor; and a power compensator
which is connected in parallel with a DC power input portion of the
inverter, wherein the power compensator includes: a power storage
device which absorbs/discharges power; a step-up/down circuit which
is connected between the DC bus bar and the power storage device
and converts a voltage level; and a control device which controls
the step-up/down circuit for exchanging DC power between the DC bus
bar and the power storage device, and the control device performs:
(A) a power compensation process A in which in a period when
DC-power-supply power exchanged by the DC power supply exceeds a
DC-power-supply power running power limit determined on the basis
of power which can be supplied by the DC power supply, power
supplied from the DC power supply is reduced to the DC-power-supply
power running power limit by discharging energy stored in the power
storage device, and in a period when the DC-power-supply power is
less than a DC-power-supply regeneration power limit determined on
the basis of power which can be regenerated by the DC power supply,
power regenerated to the DC power supply is suppressed to the
DC-power-supply regeneration power limit by charging the power
storage device with energy; and a power storage adjustment process
B including: (B-1) a process in which in the period when the
DC-power-supply power exceeds the DC-power-supply power running
power limit, energy of the power storage device is discharged to
the inverter or the DC power supply such that a voltage of the
power storage device becomes a predetermined value; (B-2) a process
in which in the period when the DC-power-supply power is less than
the DC-power-supply regeneration power limit, the power storage
device is charged with energy from the inverter or the DC power
supply such that the voltage of the power storage device becomes a
predetermined value; and (B-3) a process in which in a period when
the DC-power-supply power is not less than the DC-power-supply
regeneration power limit and is not greater than the
DC-power-supply power running power limit, the power storage device
is charged in a power range of a difference between the
DC-power-supply power running power limit and required power of the
inverter, or is discharged in a power range of a difference between
the required power of the inverter and the DC-power-supply
regeneration power limit, such that the voltage of the power
storage device becomes a predetermined value.
2. The AC motor driving apparatus according to claim 1, wherein the
control device has a first threshold which is set to a value less
than the DC-power-supply power running power limit and a second
threshold which is set to a value greater than the DC-power-supply
regeneration power limit, and in the power compensation process A
of the control device, in a period when the DC-power-supply power
exceeds the first threshold, the power supplied from the DC power
supply is suppressed to the DC-power-supply power running power
limit by discharging the energy stored in the power storage device,
and in a period when the DC-power-supply power is less than the
second threshold, the power regenerated to the DC power supply is
suppressed to the DC-power-supply regeneration power limit by
charging the power storage device with energy.
3. The AC motor driving apparatus according to claim 1, wherein the
control device includes a storage section which stores a voltage
instruction pattern for the power storage device in the power
storage adjustment process B, the voltage instruction pattern being
calculated on the basis of a power pattern representing a change of
power required by the inverter or a power pattern for the power
compensation process A representing a change of
charging/discharging power of the power storage device in the power
compensation process A, and the control device performs
charging/discharging of the power storage device in the power
storage adjustment process B on the basis of the voltage
instruction pattern.
4. The AC motor driving apparatus according to claim 3, wherein the
control device: includes a communication processing section which
communicates with an external control device which determines an
operation of the AC motor; receives, from the external control
device, the power pattern, the power pattern for the power
compensation process A, or the voltage instruction pattern for the
power storage device; and performs charging/discharging of the
power storage device in the power storage adjustment process B on
the basis of the received information.
5. The AC motor driving apparatus according to claim 1, wherein the
control device limits a charging/discharging current of the power
storage device in the power compensation process A on the basis of
a predetermined charging/discharging current limit for the power
storage device.
6. The AC motor driving apparatus according to claim 5, wherein the
control device limits a charging/discharging current of the power
storage device in the power storage adjustment process B on the
basis of the charging/discharging current limit for the power
storage device.
Description
TECHNICAL FIELD
The present invention relates to an AC motor driving apparatus
which converts DC power from a DC power supply to AC power by an
inverter and supplies the AC power to an AC motor, and particularly
relates to an AC motor driving apparatus including a power
compensator which performs compensation of power for DC power
supplied to an inverter.
BACKGROUND ART
A conventional AC motor driving apparatus includes a DC power
supply which supplies DC power, an inverter which converts the DC
power from the DC power supply to AC power and supplies the AC
power to an AC motor, and a control device for them. As the DC
power supply used in this case, there are various types depending
on application of the AC motor. For example, when the AC motor is a
motor for driving an electric rolling stock, a DC wire is the DC
power supply. In addition, when the AC motor is an industrial motor
such as a servomotor, AC power from a power supply system is
rectified by a converter to supply DC power.
Meanwhile, AC motors having various characteristics have been put
into production. Among them, there is an AC motor having two types
of rated outputs, short-time rated output and continuous rated
output. In such a case, the short-time rated output of the AC motor
is set so as to have a very high value as compared to the
continuous rated output. The reason is that, for example, in the
case where the AC motor is operated to accelerate or decelerate,
when the AC motor operates at the short-time rated output only for
a relatively short time such as during acceleration or
deceleration, it is possible to reduce the time required for speed
change. In this case, it is necessary to select the DC power supply
and the inverter according to the short-time rated output, and,
accordingly, a power supply facility also needs to have a capacity
which can tolerate the short-time rated output.
However, when an actual operation is performed, peak power is
equivalent to the short-time rated output, but the average power
may be decreased on a time average basis. Thus, a problem arises
that the prepared power supply facility is not effectively used.
And, due to the preparation of the power supply facility according
to the short-time rated output, it may be difficult to introduce
the apparatus.
For solving such a problem, various techniques have conventionally
been developed. For example, in the conventional technique in
Patent Document 1 described below, a power compensator including a
capacitor which stores power and a step-up/down circuit which
converts a voltage level is provided, and when power or a current
used by an inverter or a converter exceeds a predetermined value,
energy is discharged from the power compensator to suppress a
current peak of a DC power supply. In addition, in the conventional
technique in Patent Document 2 described below, when the voltage or
current of a DC bus bar connected to an inverter exceeds a
predetermined value, power of a power compensator is discharged or
absorbed.
When such a conventional technique disclosed in Patent Document 1
or 2 is applied, power stored in the power compensator is
discharged while demand for peak power occurs, thereby enabling AC
motor driving to be realized at the short-time rated output over
the limitation on the capacity of the power supply facility. Patent
Document 1: Japanese Patent No. 4339916 Patent Document 2: Japanese
Laid-Open Patent Publication No. 2005-328618
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
However, the conventional techniques disclosed in Patent Documents
1 and 2 described above have the following problems. Specifically,
in these Patent Documents 1 and 2, when demand for power exceeding
a magnitude that can be exchanged by the DC power supply occurs in
a power running state, power is discharged from the power
compensator. Then, in order to meet such power demand, it is
necessary to previously charge the power compensator as
appropriate. In this case, the charging is performed mainly in a
regeneration state where energy returns from the AC motor.
Here, when power demands in power running and in regeneration occur
alternately with the substantially same frequency, charging and
discharging of power with respect to the power compensator are
balanced and thus almost no problem arises. However, when power
demand in the same state such as only in power running or only in
regeneration is continued, power stored in the power compensator
becomes short or excessive. For example, in the case where a
regeneration state is less frequent and a power running operation
is mainly performed, such as in the case where the AC motor is
applied to a fan or a pump or is used for cutting by a working
machine, a problem prominently appears that the power stored in the
power compensator becomes short.
In addition, for example, when compensation is performed for power
associated with acceleration or deceleration of the AC motor, the
magnitude of power demand in regeneration is smaller than the
magnitude of power demand in power running in many cases due to
loss of the AC motor, the inverter, and further the power
compensator itself. Therefore, when the power compensator is
charged mainly in a regeneration state as in the conventional
techniques disclosed in Patent Documents 1 and 2, the amount of
power of the power compensator tends to be short.
The problem of power shortage or power excess of the power
compensator can relatively easily be dealt with when a power
storage device, such as a capacitor, included in the power
compensator is made to have a large capacity. As a result,
problems, such as causing increase in cost, size, and weight,
arise.
The present invention has been made to solve the problems described
above, and an object of the present invention is to provide an AC
motor driving apparatus which allows reliable power compensation to
always be realized even when power demand in the same state such as
power running or regeneration is continued, even if a power storage
device, such as a capacitor, included in a power compensator is not
made to have a large capacity.
Solution to the Problems
According to the present invention, an AC motor driving apparatus
includes: a DC power supply which supplies DC power; an inverter
which converts the DC power to AC power and supplies the AC power
to an AC motor; and a power compensator which is connected in
parallel with a DC power input portion of the inverter. The power
compensator includes: a step-up/down circuit which converts a
voltage level of the DC power; a power storage device which
absorbs/discharges power; and a control device which controls the
step-up/down circuit and the power storage device, and the control
device performs: a power compensation process A in which power of
the power storage device is discharged or absorbed such that the
absolute value of DC power exchanged by the DC power supply does
not exceed a DC power supply power limit determined on the basis of
a characteristic of the DC power supply; and a power storage
adjustment process B in which the power is discharged or absorbed
such that a voltage of the power storage device becomes a
predetermined value.
Effect of the Invention
According to the present invention, in driving the AC motor, when
power demand for the AC motor exceeds a predetermined value, the
power compensator charges/discharges the power storage device to
perform power compensation, and when power compensation is
unnecessary, the power compensator obtains a power allowance of
power inputted and outputted to the power storage device on the
basis of the DC power supply power limit and required power of the
inverter, and performs auxiliary charge of the power storage device
within the range of the power allowance to store power. Thus, even
if the power storage device, such as a capacitor, included in the
power compensator is not made to have a large capacity, power
compensation can be always reliably realized even when power demand
in the same state such as power running or regeneration is
continued.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a configuration diagram showing the entirety of an AC
motor driving apparatus according to Embodiment 1 of the present
invention.
FIG. 2 is a circuit configuration diagram showing a DC power supply
and an inverter in the AC motor driving apparatus.
FIG. 3 is a circuit configuration diagram showing other types of a
DC power supply and an inverter in the AC motor driving
apparatus.
FIG. 4 is a circuit configuration diagram of a step-up/down circuit
in the AC motor driving apparatus.
FIG. 5 is a circuit configuration diagram of another type of a
step-up/down circuit in the AC motor driving apparatus.
FIG. 6 is a configuration diagram showing a detail of a control
device provided in a power compensator of the AC motor driving
apparatus.
FIG. 7 is a configuration diagram showing a detail of a DC power
calculation section included in the control device in FIG. 6.
FIG. 8 is a configuration diagram showing a detail of a power
compensation control section included in the control device in FIG.
6.
FIG. 9 is a configuration diagram showing a detail of a constant
voltage control section included in the control device in FIG.
6.
FIG. 10 is a time chart showing a series of operations associated
with a power compensation process A in the case where a power
storage adjustment process B is performed in the power compensation
control section included in the control device in FIG. 6.
FIG. 11 is a configuration diagram showing a detail of a current
instruction addition section included in the control device in FIG.
6.
FIG. 12 is a configuration diagram showing a detail of a current
control section included in the control device in FIG. 6.
FIG. 13 is a time chart showing an example of operation explanation
of the power compensation process A and the power storage
adjustment process B during power running of an AC motor in the
power compensator in Embodiment 1 of the present invention.
FIG. 14 is a circuit configuration diagram of a step-up/down
circuit in an AC motor driving apparatus according to Embodiment 2
of the present invention.
FIG. 15 is a time chart for illustrating a voltage instruction
setting operation for a power storage device by a power compensator
included in an AC motor driving apparatus according to Embodiment 3
of the present invention.
FIG. 16 is a time chart for illustrating another voltage
instruction setting operation for the power storage device by the
power compensator included in the AC motor driving apparatus
according to Embodiment 3 of the present invention.
FIG. 17 is a configuration diagram showing a detail of a power
storage device voltage instruction generation section provided
within the power compensator in the AC motor driving apparatus
according to Embodiment 3 of the present invention.
FIG. 18 is a configuration diagram showing a detail of a power
storage device voltage instruction generation section provided
within a power compensator in an AC motor driving apparatus
according to Embodiment 4 of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
FIG. 1 is a configuration diagram showing an AC motor driving
apparatus according to Embodiment 1 of the present invention and an
AC motor driven by the AC motor driving apparatus.
DC power outputted from a DC power supply 1 is supplied to an
inverter 3 via a DC bus bar 2. DC-to-AC power conversion is
performed by the inverter 3 to supply appropriate AC power to an AC
motor 4. A power compensator 5 is connected in parallel with the DC
bus bar 2 which electrically connects the DC power supply 1 to the
inverter 3, and mainly includes a step-up/down circuit 10, a power
storage device 15, a control device 16, and voltage and current
detectors 6, 7, 11, and 12.
As the DC power supply 1, a diode converter or a PWM converter
which rectifies AC power from a power supply system is used. For
example, in the case where the AC motor 4 is used for driving an
electric rolling stock, power supplied from a DC wire is received,
and thus the DC wire corresponds to the DC power supply.
FIG. 2 shows a configuration in the case where the diode converter
is used as the DC power supply 1, and FIG. 3 shows a configuration
in the case where the PWM converter is used as the DC power supply
1. It is noted that the inverter 3 is also shown together therein.
The diode converter shown in FIG. 2 cannot return power to the
power supply system side, and thus a resistor R1 for regeneration
and a switching device Q1 are provided to process regenerative
power that cannot be absorbed by the power compensator 5. In
addition, the PWM converter shown in FIG. 3 can control a current
flowing to the power supply system and can control power used by
itself.
The step-up/down circuit 10 performs voltage level conversion
between the DC bus bar 2 and the power storage device 15 to
exchange power therebetween. As the step-up/down circuit 10 in this
case, there is, for example, a chopper circuit which includes
switching devices Q2 and Q3, a reactor L1, and a capacitor C3 for
smoothing as shown in FIG. 4, and a step-down operation for the DC
bus bar 2 side is performed. In addition, depending on operating
conditions and the specifications of the power storage device 15,
the voltage of the power storage device 15 may be higher than the
voltage of the DC bus bar 2. In such a case, a circuit which
includes switching devices Q4 to Q7, a reactor L2, and a capacitor
C4 for smoothing and is capable of performing a step-up/down
operation as shown in FIG. 5 can be used.
The power storage device 15 stores energy, and capacitors such as
an electrolytic capacitor and an electrical double-layer capacitor,
batteries such as a lithium ion battery, and the like correspond to
the power storage device 15.
The control device 16 outputs a switching instruction 17 for
controlling the step-up/down circuit 10, on the basis of
information such as voltage and current signals of the DC bus bar 2
and the power storage device 15 which are acquired from the
detectors 6, 7, 11, and 12, and discharges power of the power
storage device 15 to the DC bus bar 2 side or charges the power
storage device 15.
In particular, in Embodiment 1, when the absolute value of the DC
power inputted and outputted from the DC power supply 1 to the DC
bus bar 2 is equal to or greater than a predetermined value, the
control device 16 performs power compensation by the power
compensator 5 such that the power inputted and outputted from the
DC power supply 1 to the DC bus bar 2 does not exceed a power limit
value of the DC power supply 1, namely, an allowable range
(hereinafter, this process is referred to as a power compensation
process A).
However, only with the power compensation process A,
excess/shortage of an amount of power of the power storage device
15 occurs in the case where power demand in the same state such as
power running or regeneration is continued. Thus, in addition to
the power compensation process A, the control device 16 performs a
charging/discharging operation on the power storage device 15
according to need (hereinafter, this process is referred to as a
power storage adjustment process B). A range of power that can be
supplied by the DC power supply 1 in the case where the power
storage adjustment process B is performed is determined by a degree
of a power allowance with respect to the power storage device 15
which is based on the difference between a power limit of the DC
power supply 1 and required power of the inverter 3 as described in
detail later.
A specific example of the entire configuration of the control
device 16 is shown in FIG. 6.
The control device 16 includes a DC power calculation section 16A,
a power compensation control section 16C, a constant voltage
control section 16E, a current instruction addition section 16G, a
current control section 16I, and a PWM control section 16K.
Here, the DC power calculation section 16A receives an output
current (i.e., a DC bus bar current) 8 of the DC power supply 1 and
an output voltage (i.e., a DC bus bar voltage) 9 of the DC power
supply 1 which are detected by the detectors 6 and 7, and
multiplies both 8 and 9 to calculate a DC-power-supply power 16B.
In addition, the power compensation control section 16C receives
the DC-power-supply power 16B and outputs a current instruction 16D
for performing the power compensation process A.
Meanwhile, the constant voltage control section 16E receives the
DC-power-supply power 16B obtained by the DC power calculation
section 16A and a power-storage-device current 13 and a
power-storage-device voltage 14 which are obtained by the detectors
11 and 12, and outputs a current instruction 16F for performing the
power storage adjustment process B.
In order that the power compensation process A and the power
storage adjustment process B are smoothly performed without
interruption, the current instruction addition section 16G adds
both current instructions 16D and 16F and outputs the current
instruction resulting from the addition, as a current instruction
16H to the power storage device 15.
The current control section 16I outputs a voltage instruction 16J
for performing current control such that the power-storage-device
current 13 detected by the detector 11 coincides with the current
instruction 16H in order that the power storage device 15 is
charged and discharged with a required current corresponding to the
current instruction 16H.
The PWM processing control section 16K outputs the switching
instruction 17 for controlling the voltage of the step-up/down
circuit 10, on the basis of the voltage instruction 16J provided
from the current control section 16I in order that the power
storage device 15 is charged and discharged with a required
current. The step-up/down circuit 10 operates on the basis of the
switching instruction 17.
Next, the configuration of each section of the control device 16
described above will be described in more detail.
First, as shown in FIG. 7, the DC power calculation section 16A
calculates the product of the DC-bus-bar current 8 and the
DC-bus-bar voltage 9, which are detected by the detectors 6 and 7,
by a multiplier 18 to obtain the DC-power-supply power 16B, and
outputs the DC-power-supply power 16B. It is noted that when the
DC-bus-bar voltage 9 is very low, the DC power calculation section
16A corrects the DC-power-supply power 16B by multiplying the
DC-power-supply power 16B by a correction coefficient k1 which is
previously set in a correction coefficient table 20 and corresponds
to the magnitude of the DC-bus-bar voltage 9, by a multiplier 19.
This is due to the following reason.
When a load of the AC motor 4 is increased and great power demand
occurs for the inverter 3, the DC power supply 1 uses a high
current. At that time, when the DC power supply 1 performs an
operation of limiting or cutting a used current for protecting
itself, the voltage of the DC bus bar 2 varies. For example, in the
DC power supply 1 as shown in FIGS. 2 and 3, capacitors C1 and C2
provided on the DC bus bar 2 side are charged and discharged, and
the voltage of the DC bus bar 2 varies. The power inputted to and
outputted from the DC power supply 1 during a period when the
capacitors C1 and C2 are charged and discharged is the same value
as the power demand of the inverter 3, but the voltage of the DC
bus bar 2 rapidly decreases or rapidly increases due to the above
operation. Thus, even though power demand required for power
compensation occurs on the AC motor 4 side, an operation of the
power compensation process A may not be immediately started. As a
result, the responsiveness of the power compensation process A may
be deteriorated and appropriate power compensation may not be
performed. The correction coefficient table 20 provided in the DC
power calculation section 16A is intended to eliminate this, and
serves to make the DC-power-supply power 16B apparently great with
respect to rapid decrease or increase in the DC-bus-bar voltage 9,
thereby causing the power compensation process A to be immediately
performed.
Next, a detailed configuration of the power compensation control
section 16C is shown in FIG. 8. It is noted that, here, for
convenience of explanation, a positive direction of current/voltage
of each section detected within the power compensator 5 is
indicated as the direction of an arrow. Therefore, the
DC-power-supply power 16B is positive in a power running state. In
addition, when the-power-storage device current 13 flows in the
positive direction, the power storage device 15 is charged. In
other words, the power storage device 15 absorbs power.
The power compensation control section 16C receives the
DC-power-supply power 16B obtained by the DC power calculation
section 16A, and determines by comparison by a DC-power-supply
power comparison determination section 32 whether or not the
absolute value of the DC-power-supply power 16B is equal to or
greater than a threshold PowTH which is previously set in
consideration of a range of DC power that can be supplied by the DC
power supply 1.
If the absolute value of the DC-power-supply power 16B is less than
the threshold PowTH, the power demand of the AC motor 4 can be met
by the DC-power-supply power 16B supplied from the DC power supply
1, and the power compensation process A is unnecessary. Thus, the
DC-power-supply power comparison determination section 32 connects
each of both switches SWa and SWb to a "0" output side. In other
words, the current instruction 16D for the power compensation
process A is not outputted.
On the other hand, if the absolute value of the DC-power-supply
power 16B is equal to or greater than the threshold PowTH, the
power demand of the AC motor 4 cannot be met only by the
DC-power-supply power 16B supplied from the DC power supply 1, and
the power compensation process A by the power compensator 5 is
required. Thus, the DC-power-supply power comparison determination
section 32 connects each of the switches SWa and SWb to a loop side
in which integrating control is mainly performed.
A DC-power-supply power running power limit LM1a (positive value)
and a DC-power-supply regeneration power limit LM1b (negative
value), which are upper and lower limits of suppliable power which
are determined according to power running and regeneration states
and on the basis of the characteristics of the DC power supply 1,
are previously set in the power compensation control section 16C.
When each of the switches SWa and SWb is connected to the loop side
in which integrating control is mainly performed as described
above, each of subtractors 33a and 33b of the power compensation
control section 16C calculates the difference between the
DC-power-supply power running power limit LM1a or the
DC-power-supply regeneration power limit LM 1b and the inputted
DC-power-supply power 16B, and integrating control is performed by
each of integrators 34a and 34b using the difference, and the
current instruction 16D to the power storage device 15 is
outputted.
In this case, limiters 35a and 35b are provided in the middles of
loops of the integrating control of the integrators 34a and 34b,
respectively. These limiters 35a and 35b are intended to prevent
signals from being excessively accumulated in the integrators 34a
and 34b when the power compensation process A is unnecessary, and
are also intended to suppress the current instruction 16D such that
the current instruction 16D falls within a predetermined range in
order that a current with which the power storage device 15 is
charged/discharged does not exceed a power-storage-device
discharging current limit LM2a (negative value) and a
power-storage-device charging current limit LM2b (positive value),
which are lower and upper limits of a chargeable/dischargeable
current which are previously set on the basis of the
characteristics of the power storage device 15. In particular, when
the operation of the power compensation process A shifts from ON to
OFF, the limiters 35a and 35b smoothly attenuate signals
accumulated in the integrators 34a and 34b to prevent chattering.
In addition, the power storage device 15 includes a battery or a
capacitor as described above, and they each have an appropriate
temperature range and there is an appropriate power-stored state,
namely, an appropriate current recommended by a voltage value of
the power storage device 15 for efficiently exchanging electric
energy. Thus, in order to use the power storage device 15 in an
appropriate state, it is necessary to limit a current during
charging/discharging. This is achieved by controlling the current
limit values LM2a and LM2b which are set in the limiters 35a and
35b, respectively.
It is noted that the threshold PowTH which is previously set in the
DC-power-supply power comparison determination section 32 is set to
a value that is slightly lower than the absolute value of each of
the power running and regeneration power limits LM1a and LM1b of
the DC power supply 1. This is because if the threshold PowTH is
set to the same value as the absolute value of each of the power
running and regeneration power limits LM1a and LM1b, chattering
occurs in the integrators 34a and 34b before and after the absolute
value of the DC-power-supply power 16B becomes equal to the
threshold PowTH, and it is necessary to prevent this chattering. In
addition, here, the threshold PowTH is set to the same value for
both the power running side and the regeneration side, but
different thresholds may be set therefor. For example, in the case
where the DC power supply 1 is the diode converter shown in FIG. 2,
regenerative power is consumed by the resistor R1. Thus, a
processable amount thereof is often smaller than that of power
running power, and the threshold PowTH is set to different values
for the power running side and the regeneration side.
Next, a detailed configuration of the constant voltage control
section 16E is shown in FIG. 9.
The constant voltage control section 16E calculates the current
instruction 16F for performing the power storage adjustment process
B. Specifically, in order that the voltage of the power storage
device 15 becomes a predetermined value, the constant voltage
control section 16E calculates, by a subtractor 40, the difference
between the power-storage-device voltage 14 detected by the
detector 12 at the present time and a voltage instruction 16M which
is a control target value of a power storage voltage for the power
storage device 15 and is provided from a power-storage-device
voltage instruction generation section 16L, and performs
integrating control by an integrator 41 using the difference, to
obtain the current instruction 16F for performing constant voltage
control on the power storage device 15. In the integrating control
by the integrator 41, it is necessary to apply, to the power
storage device 15, power within a range of power that can be used
by the DC power supply 1, namely, within a range where there is a
power allowance in the DC power supply 1. Thus, it is necessary to
provide, to the integrator 41, a current limit which defines a
limit corresponding to the power allowance of the DC power supply
1.
Therefore, first, the power allowance of the DC power supply 1 is
calculated. For this, an inverter power Wiv is obtained by
calculating, by a subtractor 43, the difference (=16B-Wb) between
the above DC-power-supply power 16B obtained by the DC power
calculation section 16A and a power-storage-device power Wb
obtained by multiplying the power-storage-device current 13 and the
power-storage-device voltage 14, which are obtained by the
detectors 11 and 12, by a multiplier 42. Next, the differences
between the inverter power Wiv and the above DC-power-supply power
running power limit LM1a (positive value) and DC-power-supply
regeneration power limit LM1b (negative value), which are the upper
and lower limits of suppliable power determined according to the
power running and regeneration states of the DC power supply 1, are
calculated by subtractors 44a and 44b, respectively. The reason why
the power Wiv of the inverter 3 is used is that the power of the DC
power supply 1 varies in response to the operation of the constant
voltage control section 16E itself and thus cannot be directly
identified only by detection of the DC-power-supply power 16B.
Then, each of the power differences obtained by the subtractors 44a
and 44b becomes the power allowance of the DC power supply 1. Next,
each power difference is divided by the power-storage-device
voltage 14 by a divider 45a or 45b to obtain a current limit
corresponding to the power allowance of the DC power supply 1.
Limiters 46a and 46b provided at stages immediately after the
divisions by the dividers 45a and 45b are intended to prevent
interference with the power compensation process A. For example,
when the power difference obtained by the subtractor 44a is
negative, the inverter power Wiv required by the inverter 3 exceeds
the supply capacity of the DC power supply 1 and there is no power
allowance, and therefore, it is in a state where the power
compensation process A should be performed, not in a state where
the power storage adjustment process B should be performed. Thus,
when the power difference obtained by the subtractor 44a is
negative, output is eliminated by the limiter 46a. The same applies
to the case of the regeneration state.
Through the above process, the current limits for the power storage
device 15 corresponding to the power allowance of the DC power
supply 1 are obtained. The current limits should not exceed the
above power-storage-device discharging current limit LM2a (negative
value) and power-storage-device charging current limit LM2b
(positive value), which are determined on the basis of the
characteristics of the power storage device 15, and thus the
current limit whose absolute value is smaller is selected by
selection circuits 47a and 47b. The current limit selected by the
selection circuits 47a and 47b is provided to a limiter 48 provided
in the middle of a loop of the integrating control of the
integrator 41, whereby the current limit corresponding to the power
allowance of the DC power supply 1 is provided to the integrator
41.
With such a configuration, the power storage adjustment process B
can be performed without disturbing the power compensation process
A. In other words, the power compensation process A can be
preferentially performed. Furthermore, the power storage adjustment
process B can be performed within the range of the power allowance
of the DC power supply 1, and it is also possible to use the
inverter power Wiv.
Here, for reducing the number of current detectors, the inverter
power Wiv is calculated from the DC-power-supply power 16B and the
power-storage-device power Wb by using the subtractor 43. In
addition, power from the power storage device 15 has loss by the
step-up/down circuit 10, and thus loss correction is performed by a
provided step-up/down circuit loss correction circuit 49 for
deriving the inverter power Wiv. It is noted that since it is only
necessary to be able to calculate the inverter power Wiv, a current
detector may be provided on the input side of the inverter 3 and
the inverter power Wiv may be obtained by multiplication with the
DC bus bar 2. In addition, although depending on an operating state
or a purpose, if the voltage instruction 16M for the power storage
device 15 in the power-storage-device voltage instruction
generation section 16L is a rated voltage Vf of the power storage
device 15, power compensation can be performed emphasizing power
compensation in power running.
It is noted that as the power running and regeneration power limit
values LM1a and LM1b of the DC power supply 1 described with
reference to FIGS. 8 and 9, predetermined rated power values are
used in the case where the DC power supply 1 is the diode converter
shown in FIG. 2. In addition, in the case where the DC power supply
1 is the PWM converter shown in FIG. 3, for the operations of the
power compensation control section 16C and the constant voltage
control section 16E shown in FIGS. 8 and 9, the power running and
regeneration power limit values LM1a and LM1b are previously set to
values slightly lower than the predetermined rated power values, or
a power limit value of the PWM converter itself is previously set
to a value slightly higher than a predetermined rated value. This
becomes a measure for normally performing the processes shown in
FIGS. 8 and 9, because the PWM converter can control and limit
power by itself.
Next, a series of operations associated with the power compensation
process A in the case where the power storage adjustment process B
is performed in the power compensation control section 16C will be
described with reference to FIG. 10.
As shown in FIG. 10(a), the inverter power Wiv changes with time.
In this case, the difference W1 between the inverter power Wiv and
the DC-power-supply power running power limit LM1a becomes a power
allowance Ma which can be used for the power storage adjustment
process B in a direction in which the power storage device 15 is
charged as shown in FIG. 10(b). In addition, the difference W2
between the inverter power Wiv and the DC-power-supply regeneration
power limit LM1b becomes a power allowance Mb which can be used for
the power storage adjustment process B in a direction in which the
power storage device 15 is discharged as shown in FIG. 10(b).
Each period indicated by a reference character TA in FIG. 10 is a
period when the inverter power Wiv exceeds the absolute value of
each of the power running and regeneration power limit values LM1a
and LM1b of the DC power supply 1, and is a state where the power
compensation control section 16C operates. In this case, although
the power compensation process A and the power storage adjustment
process B are different in priority from each other, the operations
of both processes A and B are possible at the same time depending
on the direction of power.
For example, in the period indicated by Tc in FIG. 10, it is in a
regeneration state where power returns from the inverter 3, and the
power compensation process A is included, in addition the power
storage adjustment process B in a direction in which the power
storage device 15 is charged can be performed at the same time. The
power compensation process A and the power storage adjustment
process B may be exclusively performed with reference to the power
allowance of the DC power supply 1. However, when the power storage
adjustment process B described above is caused to be always
performed and a process of adjusting the current instruction 16F in
the power storage adjustment process B by the limiter 48 is
performed, the voltage of the power storage device 15 can be
quickly shifted to a predetermined value which is a target.
Next, a detailed configuration of the current instruction addition
section 16G is shown in FIG. 11.
In order that the power compensation process A and the power
storage adjustment process B are smoothly performed without
interruption, the current instruction addition section 16G adds, by
an adder 50, the current instruction 16D for the power storage
device 15 provided from the power compensation control section 16C
and the current instruction 16F for power-storage-device constant
voltage control provided from the constant voltage control section
16E. When the current instruction 16H obtained thus is a minute
value, the current of the power storage device 15 may tend to be in
a hunting state due to the process of the current control section
16I at the subsequent stage. Thus, when the current instruction is
minute, a process of forcibly clamping the current instruction 16H
to "0" is performed by a clamping process section 51 provided
within the current instruction addition section 16G. In addition,
the current instruction 16H for the power storage device 15 is
limited by a provided limiter 52 so as to not exceed each of the
current limits LM2a and LM2b of a charging/discharging current
allowable for the power storage device 15, and then is
outputted.
Next, a detailed configuration of the current control section 16I
is shown in FIG. 12.
The current instruction 16H for the power storage device 15
obtained by the current instruction addition section 16G is
inputted to the current control section 16I. Then, the current
control section 16I calculates, by a subtractor 60, the difference
between the current instruction 16H and the power-storage-device
current 13 detected by the detector 11, performs PI control by a PI
control section 61 on the basis of the difference, and calculates
the voltage instruction 16J for the step-up/down circuit 10. At
that time, application of an excessive voltage to the power storage
device 15 is prevented by voltage limiters 62 and 63 which are
provided in the middle of a control loop of the PI control section
61 and on the output side of the PI control section 61,
respectively, and which limit a voltage applied to the power
storage device 15 such that the voltage does not exceed a
power-storage-device voltage limit LM3 which is an upper limit of a
voltage applicable to the power storage device 15. By the voltage
limiters 62 and 63, a process can be realized which smoothly shifts
from constant current charging/discharging to constant voltage
charging/discharging. It is noted that in the PI control section 61
in FIG. 12, 61a indicates a proportional gain, and 61b indicates an
integral gain.
In FIG. 12, the lower limits of the voltage limiters 62 and 63 are
set to "0", but may be set as appropriate according to the type,
the state (SOC), or the like of the power storage device 15 in a
state which is not during initial charging. In addition, when the
current instruction 16H is "0", none of the processing operations
of the power compensation process A and the power storage
adjustment process B is performed, switches 65 and 66 are switched
by a switch-switching circuit 64, and the power-storage-device
voltage 14 is selectively outputted instead of output of an
integrator 67 within the PI control section 61 and the output of
the voltage instruction 16J. Thus, an effect is provided that a
current control operation can be performed immediately when a next
current instruction for charging/discharging the power storage
device 15 is issued.
Next, the PWM control section 16K will be described in detail.
The PWM control section 16K calculates a duty ranging from "0" to
"1" according to the current instruction 16H provided from the
current instruction addition section 16G, the voltage instruction
16J provided from the current control section 16I, and a reference
voltage, and performs a PWM process by carrier comparison. Here,
the reference voltage is the DC-bus-bar voltage 9. In this case,
each of the switching devices on the P side and the N side
constituting the step-up/down circuit 10 may be operated in a
complementary manner, or, for example, when the current instruction
16H for the power storage device 15 is positive, the switching
device on the N side may always output an OFF instruction. Thus,
the driving circuit of the switching device to be turned off can be
stopped, leading to reduction of power loss. In addition, it is not
necessary to provide a dead time for preventing short circuit, and
a controllable voltage range can be expanded. It is noted that when
the voltage instruction 16J provided from the current control
section 16I is zero, the PWM control section 16K outputs an
instruction to turn off both of the switching devices on the P side
and the N side of the step-up/down circuit 10.
With regard to the control device 16 of the power compensator 5
which has the above configuration and operation, an example of the
power compensation process A and the power storage adjustment
process B during power running of the AC motor 4 is shown in FIG.
13. Here, FIG. 13(a) shows a relationship between the inverter
power Wiv and the DC-power-supply power 16B. FIG. 13(b) shows the
power-storage-device current 13, and FIG. 13(c) shows the
power-storage-device voltage 14.
With occurrence of power demand of the inverter 3, an operation of
the power compensation process A is started. Thus, as shown in FIG.
13(b), the power-storage-device current 13 flows in the negative
direction and discharging is performed. Here, when the power
storage adjustment process B is not performed and power demand
repeatedly occurs, an amount of power stored in the power storage
device 15 is gradually lost, and the power compensation process A
is finally disenabled. On the other hand, in Embodiment 1, after
the operation of the power compensation process A ends, an
operation of the power storage adjustment process B is mainly
performed, and an operation of charging the power storage device 15
is performed. Thus, next power demand of the inverter 3 can also be
dealt with. It is noted that as shown in FIG. 13, during operation
of the power storage adjustment process B, the DC-power-supply
power 16B is substantially equal to or less than the
DC-power-supply power running power limit LM1a.
As described above, in the AC motor driving apparatus according to
Embodiment 1, for example, when the control device 16 within the
power compensator 5 is configured as shown in FIG. 6, the power
compensation process A and the power storage adjustment process B
can be smoothly performed for the power demand required by the
inverter 3 without interfering with each other, and the power of
the DC power supply 1 does not greatly exceed the power limit
values LM1a and LM1b. Therefore, even when the AC motor 4 is
included in an apparatus such as a working machine, an electric
press, and an injection molding machine and is required to operate
at high output for a short time, the AC motor 4 can be effectively
used.
In addition, as described above, in the power storage adjustment
process B, an operation of charging/discharging the power storage
device 15 with a constant voltage is performed by using the power
allowance of the DC power supply 1. Thus, the power storage device
15 can be charged/discharged without interfering with the operation
of the power compensation process A. As a result, even when power
demand in the same direction such as in power running or in
regeneration occurs in the inverter 3, appropriate compensation is
possible. In particular, this is very effective for the case where
a power running load relatively frequently occurs, such as for a
fan, a pump, or a working machine which performs cutting.
Embodiment 2
In the power compensator 5 of the AC motor driving apparatus
according to Embodiment 1 described above, the circuit shown in
FIG. 4 or 5 is shown as an example of the step-up/down circuit 10
which performs voltage level conversion. However, depending on the
specifications of the power storage device 15, it is necessary to
suppress a flowing-in current ripple. Thus, for example, a
multiplex circuit (here, a three-phase circuit) shown in FIG. 14
can be used.
In this case, switching devices in a circuit of each multiplexed
phase may be operated according to the same switching instruction
17. In addition, when the current instruction 16H is equally
divided and the current control section 16I and the PWM control
section 16K are provided in each multiplexed phase, currents of the
multiplexed phases are equalized. In this case, when the phase of a
carrier signal used for generating the switching instruction 17 is
shifted, an effect of further reducing the current ripple is
obtained. For example, in the three-phase circuit shown in FIG. 14,
the phase is shifted by 360 degrees/3=120 degrees steps.
Embodiment 3
In the power compensator 5 of the AC motor driving apparatus
according to Embodiment 1 described above, in the power storage
adjustment process B in which the control device 16 controls the
voltage of the power storage device 15 to a constant voltage, the
voltage instruction 16M corresponding to the rated voltage Vf is
used as the control target value of the power storage voltage for
the power storage device 15. When the power required by the
inverter 3 is previously recognized, a power pattern representing
power change can be previously registered in a storage unit, such
as a nonvolatile semiconductor memory, provided in the constant
voltage control section 16E within the control device 16.
FIG. 15 is a time chart for illustrating a voltage instruction
setting operation for the power storage device 15. In this example,
the inverter power Wiv is repeated in a specific pattern in
constant cycles as shown in FIG. 15(a).
Here, by comparing the inverter power Wiv to the power running and
regeneration power limit values LM1a and LM1b of the DC power
supply 1, power (instantaneous value) patterns required for the
power compensation process A are obtained as shown in FIG. 15(b).
They are a combination of sequences of charging/discharging the
power storage device 15. When integration is performed for each
sequence, an amount of power which should be discharged or absorbed
by the power storage device 15 is recognized as shown in FIG.
15(c). In FIG. 15(c), a value indicated by each black circle
corresponds to the maximum value of the integral power amount.
The amount of power stored in the power storage device 15 and the
voltage of the power storage device 15 correspond to each other in
a one-to-one relation. Therefore, the amount of stored power can be
converted into a voltage which should be kept, according to the
characteristics of the battery or the capacitor constituting the
power storage device 15. Thus, when power demand occurs on the
power running side in the inverter 3 and power is discharged from
the power storage device 15, a voltage instruction for the power
storage device 15 can be determined from an amount of the power to
be discharged. On the other hand, when power demand occurs on the
regeneration side in the inverter 3 and power is absorbed by the
power storage device 15, a voltage instruction for the power
storage device 15 can be determined so as to ensure room for
absorbing an amount of the power to be absorbed.
In this case, at a stage prior to start of the power compensation
process A and the power storage adjustment process B, the amount of
power of the power storage device 15 needs to be previously
adjusted so as to be in a chargeable or dischargeable state. For
example, in the drawing of FIG. 15(c), reference characters X and Z
indicate sequences for the power compensation process A during
power running, and a reference character Y indicates a sequence for
the power compensation process A during regeneration. In this case,
for example, when focusing on the single sequence Z, a voltage
instruction for the power storage device 15 in the sequence Z is
previously set in an interval from the time of start of the
sequence Y to the time immediately before start of the sequence Z.
As described in above Embodiment 1, the power compensation process
A is performed preferentially over the power storage adjustment
process B. Thus, the voltage instruction for the power storage
device 15 in the sequence Z does not become interference for the
sequence Y. When the inverter power Wiv periodically changes in the
specific pattern as described above, a result of obtaining a series
of voltage instructions for the power storage device 15 provides a
power-storage-device voltage instruction table TB1 shown in FIG.
15(d).
Here, for example, the sequence X is power demand during power
running as described above, and the power storage device 15 is
discharged by the power compensation process A. At that time, it is
necessary to previously ensure an amount of power W.alpha. of the
power storage device 15 in a state where power compensation is
possible, in other words, at a stage prior to start of the sequence
X, the power-storage-device voltage 14 needs to be previously
adjusted so as to be equal to or higher than a voltage instruction
16P (a value indicated by a reference character V.alpha. in FIG.
15) designated by the power-storage-device voltage instruction
table TB1.
In this case, the actual power-storage-device voltage 14 is already
sufficiently higher than the above voltage instruction 16P
(V.alpha.) at the stage prior to the sequence X, a wasteful
discharge operation is performed for adjusting the
power-storage-device voltage 14 to the voltage instruction 16P
(V.alpha.). In order to prevent this, as shown in FIG. 15(e), a
power-storage-device voltage instruction state transition table TB2
is provided, and interval information representing required
transition of each of states V and W is previously stored therein
such that it is recognized by the power-storage-device voltage
instruction state transition table TB2 whether the
power-storage-device voltage 14 needs to be in a state of being
higher than or in a state of being lower than the voltage
instruction 16P designated by the power-storage-device voltage
instruction table TB1.
Thus, in an interval of the V state indicated by the
power-storage-device voltage instruction state transition table
TB2, it can be recognized that the power storage device voltage 14
needs to be in a state of being equal to or higher than the voltage
instruction 16P (V.alpha.) designated by the power-storage-device
voltage instruction table TB1.
In addition, the sequence Y is power demand during regeneration,
and the power storage device 15 is charged by the power
compensation process A. At that time, an amount of power W.beta. of
the power storage device 15 needs to be previously ensured in a
state where power compensation is possible. In other words, at a
stage prior to start of the sequence Y, adjustment needs to be
previously performed such that the power-storage-device voltage 14
is equal to or lower than the voltage instruction 16P (a value
indicated by a reference character V.beta. in FIG. 15) designated
by the power-storage-device voltage instruction table TB1, namely,
such that a voltage difference is ensured which is equal to or
greater than the voltage difference .DELTA.V between the rated
voltage Vf of the power storage device 15 and the voltage
instruction 16P (V.beta.) designated by the power-storage-device
voltage instruction table TB1. Therefore, in this case as well, by
using the power-storage-device voltage instruction state transition
table TB2, it can be recognized, in an interval of the state of the
reference character W indicated in the power-storage-device voltage
instruction state transition table TB2, whether the
power-storage-device voltage 14 needs to be in a state of being
equal to or lower than the voltage instruction 16P (V.beta.)
designated by the power-storage-device voltage instruction table
TB1.
It is noted that with regard to the power-storage-device voltage
instruction table TB1 and the power-storage-device voltage
instruction state transition table TB2 described with reference to
FIG. 15, a method may be adopted in which the voltage instruction
16P is previously decreased in preparation for the case of charging
the power storage device 15 in response to regeneration power
demand as shown in FIG. 16, and the rated voltage Vf of the power
storage device 15 is used as an instruction if it is not in such a
case. In this case as well, the power-storage-device voltage
instruction state transition table TB2 can be similarly set.
In the process of generating the tables TB1 and TB2 described
above, prior to an operation of the AC motor driving apparatus, a
process may be performed offline to obtain a voltage instruction
pattern for the power storage device 15 and the pattern may be
stored in a storage unit included in the control device 16, or
inverter power or power required for the power compensation process
A may be previously stored in the storage unit and the voltage
instruction 16P may be obtained online after start of an operation
of the AC motor driving apparatus.
FIG. 17 is a configuration diagram showing a detail of the
power-storage-device voltage instruction section 16L provided in
the constant voltage control section 16E within the control device
16 in the AC motor driving apparatus according to Embodiment 3.
Instead of the configuration in Embodiment 1 (see FIG. 9), the
power-storage-device voltage instruction section 16L of Embodiment
3 includes a power-storage-device voltage instruction table storage
section 16La, a power-storage-device voltage instruction state
transition table storage section 16Lb, and a synchronization time
signal generation section 16Lc.
In the power-storage-device voltage instruction table storage
section 16La, the power-storage-device voltage instruction table
TB1 shown in FIG. 15(d) or 16(d) is patterned and stored, and in
the power-storage-device voltage instruction state transition table
storage section 16Lb, the power-storage-device voltage instruction
state transition table TB2 shown in FIG. 15(e) or 16(e) is
patterned and stored. Furthermore, in the synchronization time
signal generation section 16Lc, a power pattern for the inverter 3
is stored.
The synchronization time signal generation section 16Lc receives a
power signal of the inverter 3 and a timer signal, collates these
signals with a built-in power table for the inverter 3, determines
which time point in the periodical power pattern for the inverter 3
the present time corresponds to, and outputs the time point as an
in-cycle time signal 16Q. As the power signal of the inverter 3,
the signal Wiv described in Embodiment 1 is used. With reference to
the in-cycle time signal 16Q, information of the voltage
instruction 16P is time-sequentially read out from the
power-storage-device voltage instruction table TB1 stored in the
power-storage-device voltage instruction table storage section
16La, and interval information of each of the states V and W in the
power-storage-device voltage instruction state transition table TB2
stored in the power-storage-device voltage instruction state
transition table storage section 16Lb is also time-sequentially
read out, and these pieces of information are inputted to a voltage
instruction selection section 16Le. At the same time, the
power-storage-device voltage 14 detected by the detector 12 is also
inputted into the voltage instruction selection section 16Le. The
voltage instruction selection section 16Le refers to the interval
information of each of the states V and W in the
power-storage-device voltage instruction state transition table
TB2, selects either the power-storage-device voltage 14 or the
voltage instruction 16P designated by the power-storage-device
voltage instruction table TB1, and outputs the selected one as the
voltage instruction 16M for the power storage device 15.
For example, if an interval designated by the power-storage-device
voltage instruction state transition table TB2 is the interval of
the state of the reference character V in FIG. 15 and the
power-storage-device voltage 14 is lower than the voltage
instruction 16P read out from the power-storage-device voltage
instruction table storage section 16La, it is necessary to charge
the power storage device 15. In this case, the voltage instruction
16P read out from the power-storage-device voltage instruction
table storage section 16La is selected and outputted as the voltage
instruction 16M for the power storage device 15.
In addition, if an interval designated by the power-storage-device
voltage instruction state transition table TB2 is the interval of
the state of the reference character V in FIG. 15 and the
power-storage-device voltage 14 is higher than the voltage
instruction 16P read out from the power-storage-device voltage
instruction table storage section 16La, the power storage device 15
is in a state where required minimum power has already been stored
therein. Then, in this case, charging/discharging is not
particularly necessary, and the power-storage-device voltage 14 is
selected and outputted as the voltage instruction 16M for the power
storage device 15. By so doing, the input of the integrator 41
becomes "0" and the operation can be stopped in the constant
voltage control section 16E shown in FIG. 9.
Furthermore, if an interval designated by the power-storage-device
voltage instruction state transition table TB2 is the interval of
the state of the reference character W in FIG. 15 and the
power-storage-device voltage 14 is higher than the voltage
instruction 16P read out from the power-storage-device voltage
instruction table storage section 16La, discharging is necessary.
In this case, the voltage instruction 16P read out from the
power-storage-device voltage instruction table storage section 16La
is outputted as the voltage instruction 16M for the power storage
device 15.
Moreover, if an interval designated by the power-storage-device
voltage instruction state transition table TB2 is the period
indicated by the reference character W in FIG. 15 and the
power-storage-device voltage 14 is lower than voltage instruction
16P read out from the power-storage-device voltage instruction
table storage section 16La, a voltage difference from the rated
voltage Vf of the power storage device 15 is ensured sufficiently,
and a required minimum capacity for charging remains in the power
storage device 15. Then, in this case, charging/discharging is not
particularly necessary, and the power-storage-device voltage 14 is
selected and outputted as the voltage instruction 16M for the power
storage device 15. By so doing, the input of the integrator 41
becomes "0" and the operation can be stopped in the constant
voltage control section 16E shown in FIG. 9.
As described above, in the AC motor driving apparatus according to
Embodiment 3, when power required by the inverter 3 is previously
recognized, the voltage instruction 16M for the power storage
device 15 is derived with the power-storage-device voltage
instruction table storage section 16La and the voltage instruction
state transition table storage section 16Lb which are provided in
the constant voltage control section 16E of the control device 16
and have stored therein the power-storage-device voltage
instruction table TB1 and the power storage device voltage
instruction state transition table TB2, respectively, whereby the
power storage adjustment process B can be performed. Thus, the
power storage device 15 can be efficiently used. Therefore, the
capacity of the battery or the capacitor used for the power storage
device 15 can be reduced, and reduction of the cost and the size of
the AC motor driving apparatus can be achieved. In particular, this
is effective for the case where the same power demand repeatedly
occurs in the inverter 3.
Embodiment 4
In the power compensator 5 of the AC motor driving apparatus
according to Embodiment 3 described above, the power-storage-device
voltage instruction table storage section 16La having stored
therein the power-storage-device voltage instruction table TB1 and
the power-storage-device voltage instruction state transition table
storage section 16Lb having stored therein the power-storage-device
voltage instruction state transition table TB2 are provided as the
power-storage-device voltage instruction section 16L, and a voltage
instruction is set on the basis of information read out from these
storage sections 16La and 16Lb. However, a configuration is also
possible in which the information in the power-storage-device
voltage instruction table TB1 and the power-storage-device voltage
instruction state transition table TB2 can be acquired from an
external controller via communication.
For example, the AC motor driving apparatus used for a working
machine or the like is used in combination with a numerical
controller (NC) 71. In the numerical controller 71, a position or
speed instruction for the AC motor 4 is generated. In addition, it
can be often recognized in what manner the AC motor 4 will operate
a little later. Thus, information of power demand required by the
inverter 3 connected to the AC motor 4 can be obtained prior to an
actual operation of the AC motor 4, and an amount of power of the
power storage device 15 can be prepared according to the power
demand of the inverter 3 by using the information.
FIG. 18 shows an example of a configuration in which the
information in the power-storage-device voltage instruction table
TB1 and the power-storage-device voltage instruction transition
table TB2 can be acquired from the outside of the AC motor driving
apparatus via communication.
Specifically, the numerical controller 71 is used as an external
controller, and in the numerical controller 71, power of the AC
motor 4 is estimated from the position/speed instruction, the used
state, or the like of the AC motor 4, and power of the inverter 3
is obtained in consideration of power loss in the inverter 3.
Furthermore, the power-storage-device voltage instruction table TB
1 and the power-storage-device voltage instruction state transition
table TB2 are created by using the process described in above
Embodiment 3, and instruction information of the voltage
instruction 16P in the power-storage-device voltage instruction
table TB1 and information of each of the intervals V and W in the
power-storage-device voltage instruction state transition table TB2
are inputted to the voltage instruction selection section 16Le via
a communication line 72 and a communication processing section 72
as communication means. Then, the power storage adjustment process
B is performed in the control device 16 of the power compensator 5
on the basis of these pieces of inputted information.
It is noted that the voltage instruction 16P and the information of
each of the intervals V and W may not be acquired from the
numerical controller 71, and power information of the inverter 3, a
position/speed instruction signal and a used state operation
instruction signal of the AC motor 4, and the like may be acquired.
In this case, the process of creating information in the
power-storage-device voltage instruction table TB 1 and the
power-storage-device voltage instruction state transition table
TB2, which process is performed in the numerical controller 71, is
performed in the control device 16 of the AC motor driving
apparatus.
Alternatively, instead of the synchronization time signal
generation section 16Lc described in Embodiment 3, the in-cycle
time signal 16Q or a synchronization trigger signal giving
notification of start of a power pattern for the inverter 3 or
state change in TB2 shown in FIG. 15 or 16 may be acquired from the
numerical controller 71, and the in-cycle time signal 16Q may be
generated on the basis of this signal. With this configuration, it
is unnecessary to include the power pattern for the inverter 3.
As described above, according to Embodiment 4, an amount of power
of the power storage device 15 can be previously prepared according
to power demand of the inverter 3. Thus, the power storage device
15 can be efficiently used. Therefore, the capacity of the battery
or the capacitor used for the power storage device 15 can be
reduced, and reduction of the cost and the size of the AC motor
driving apparatus can be achieved. In particular, this is effective
for the case of being connected to an external controller such as
the numerical controller 71.
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